Humans aren't known for being the kindest of creatures.
We are the only species to go to full on war with each other, slaughter thousands of our own species in minutes.
We have dropped nukes on each other, tortured each other and have generally shown very little regard for human or animal life.
As most people know animals are my thing and i have far more compassion for other creatures than i do for the human race. That's not to say i don't have compassion for people but rather that it is limited to a point.
To state the cruelest thing we have ever done would be a bold statement and there are so many contenders its hard to choose.
We have used poison gas on other humans, we have done horrible human experimentation, animal testing, as per my last post the meat industry in general.
We're responsible for wiping out more species and destroying more of the earth than anything else in history.
But im going to make a bold statement here and try and pick the one i think is the worst.
Imagine being able to breathe underwater and explore the depths of the ocean, imagine being able to fly above the trees and look down upon the world.
Now imagine having that taken away from you for no other reason that a human wants to keep you as a pet. To have a pretty flying creature in their yard or house. one they barely care about and fill the food and water and that's it. Unable to stretch your wings and soar, unable to explore the world, to dive and float, to drift with the wind. As natural to you as it is for us to walk.
the cruelest thing mankind ever did was to put birds in cages
Most people wont agree with me but i cant help but think of all the horrible things we've done this is the most restricting. We've taken massive amounts of birds and we took their ability to move freely from them, trapped in cages, trapped from life. Able to see the sky everyday, see other birds flying how they should but never able to do it themselves.
We are a terrible terrible species, a plague on earth and the destruction and pain we have caused is immeasurable.
If aliens exist i doubt they would contact us anyway, based on what they could observe we are essentially just one giant disease on the planet. A disease with the basic principles of preserving our own life.